1. Field of the Invention
This invention relates in general to a transducer made of write and read heads used for longitudinal or perpendicular magnetic recording at ultrahigh densities in a data storage system, and more particularly to a method and apparatus providing a stabilized top shield in a read head used for the longitudinal or perpendicular magnetic recording.
2. Description of Related Art
The heart of a computer for longitudinal recording is a magnetic disk drive which includes a rotating magnetic disk, a slider that has a transducer made of write and read heads, a suspension arm above the rotating magnetic disk, and an actuator arm that swings the suspension arm to place the transducer over selected circular tracks on the rotating magnetic disk. When the magnetic disk is stationary, the suspension arm biases the slider into contact with the surface of the magnetic disk. When the magnetic disk rotates, air is swirled by the rotating magnetic disk, causing the slider to ride on an air bearing a slight distance from the surface of the rotating magnetic disk. When the slider rides on the air bearing, the transducer is employed for writing magnetic impressions to and reading magnetic signal fields from the rotating magnetic disk. The transducer is connected to processing circuitry that operates according to a computer program to implement the write and read functions.
A commonly used write head includes top and bottom poles, a write gap, a coil, and first, second and third insulation stacks. The write gap, coil and insulation stacks are sandwiched between the top and bottom poles. The top and bottom poles are connected at the back of the write head. Current conducted to the coil induces a magnetic flux in the top and bottom poles, which cause a magnetic field to fringe out at the air bearing surface of the write head for the purpose of writing the aforementioned magnetic impressions in circular tracks on the aforementioned rotating magnetic disk.
A commonly used read head includes top and bottom shields, top and bottom gaps, a giant magnetoresistance (GMR) read sensor in a read region, and bias stack and conducting leads in side regions. The read sensor, bias stack and conducting leads are sandwiched between the top and bottom gaps, which are in turn sandwiched between the top and bottom shields. In order to perform longitudinal magnetic recording at ultrahigh densities of above 100 Gb/in2, the read head has been progressively miniaturized by fabricating the read sensor as thin as 40 nm, as narrow as 60 nm, and as short as 80 nm, and sandwiching the read sensor into the top and bottom gaps as thin as 20 nm. In order to perform stable read function, the bias stack has been progressively improved to suppress domain activities in the sense layer of the ever-smaller read sensor.
On the other hand, the top and bottom shields still remain as thick as more than 1,000 nm. These shields must be so thick to shield the read sensor from unwanted magnetic fluxes stemming from a rotating magnetic disk, and allow the read sensor to only receive needed magnetic fluxes penetrating into the gap between the shields during reading. To ensure the shield efficiency, these shields must exhibit anisotropic soft magnetic properties, such as an easy-axis coercivity (HCE) of below 10 Oe, a hard-axis coercivity (HCH) of below 2 Oe, and a uniaxial anisotropy field (HK) of below 20 Oe, and a negative saturation magnetostriction. These shields also must be magnetically stable against strong write fields during writing, in order to prevent magnetization of the shields from either rotation into unstable magnetic states or switching into an opposite stable magnetic state. The magnetization rotation induces domain activities in the shields, thus also inducing domain activities in the read sensor through magnetostatic interactions and causing noises during reading. The magnetization switching may decrease a longitudinal bias field provided by the bias stack, thus leading to difficulties in stabilizing the sense layer of the read sensor. So far, there have no special approaches to improving magnetic properties of these shields or to stabilizing the magnetizations of these shields.
Three additional challenges are posed in stabilizing the top shield than the bottom shield. First, the top shield is formed on the top gap, while the bottom shield is formed on an undercoat. Any non-ferromagnetic films underneath these shields, which may either improve magnetic properties of these shields or stabilize the magnetizations of these shields, cannot be used for the top shields due to concerns on unwanted gap increases, but can be used for the bottom leads. Second, the top shield is wavy on the gap with a very steep topography, while the bottom shield is flat on the undercoat with a very smooth topography. It is thus more difficult for domains in the top shield to function stably. Third, the top shield is closer to the top and bottom poles than the bottom shield, and its domains are thus more severely disturbed by write fields.
More stringent challenges are posed for recently extensively explored perpendicular magnetic recording. A main pole in a write head produces much stronger write fields, which more severely affect domain activities in the top and bottom shields. A tunneling magnetoresistance (TMR) read sensor in a read head requires a sense current flowing through the top or bottom shields, which induces fields and thus affects domain activities in the top and bottom shields. In addition, top and bottom shields are thinner for minimizing thermal extrusion at an air bearing surface. These thinner top and bottom shields are more susceptible to fields produced by the adjacent main pole and induced by the sense current.
It can thus be seen that a method and apparatus providing a stabilized top shield in a read head used for the longitudinal or perpendicular magnetic recording.